Review Question - QID 217032

This patient who has gradually developed dyspnea on exertion as well as productive cough and is found to have calcified perihilar lymph nodes on chest radiograph most likely has chronic silicosis. This disease is associated with workers in the sandblasting industry.

Pneumoconioses are a collection of respiratory diseases caused by an inflammatory response of the lung to the inhalation of small particles. Particles that are larger than 2 micrometers in diameter deposit in respiratory bronchioles where they are cleared by mucociliary transport. Conversely, those that are less than 2 micrometers in diameter are able to travel to alveoli where they are phagocytosed by macrophages. These macrophages are then activated in order to produce fibrogenic cytokines that result in restrictive lung disease over time. Silicosis, in particular, is caused by the inhalation of silica particles during occupations such as mining, sandblasting, and smelting.

Marrocco et al. present a review of macrophage responses to silica exposure. They discuss how phagocytosis of silica particles by macrophages results in recruitment of mitochondria to phagosomes, generation of mitochondrial reactive oxygen species, and release of cytokines (IL-1β, TNF-α, IFN-β).

Figure/Illustration A is a chest radiograph with calcified perihilar lymph nodes also known as eggshell calcifications (red circles). This finding is classically associated with chronic silicosis.

Incorrect Answers:
Answer 1: Aerospace manufacturing is associated with berylliosis, which is also a form of pneumoconiosis; however, this disease would present with noncaseating granulomas, nodular infiltrates, and enlarged lymph nodes that resemble those seen in sarcoidosis.

Answer 2: Coal mining is associated with coal workers' pneumoconiosis; however, this disease would present with centrilobular emphysema with fibrotic centers. Associated syndromes such as Caplan syndrome can also present with rheumatoid nodules in the lung.

Answer 3: Foreign travel is associated with the development of pulmonary tuberculosis. Patients with silicosis also have a higher risk of pulmonary tuberculosis; however, this patient is not likely to have this superimposed disease because he does not have constitutional symptoms such as fever, chills, weight loss, or night sweats.

Answer 5: Shipbuilding is associated with the development of asbestosis, which is also a form of pneumoconiosis; however, this disease would present with calcified pleural plaques in the diaphragm and posterolateral mid lung.

Bullet Summary:
Silicosis is caused by an inflammatory response to the phagocytosis of silica dust by macrophages in the alveoli.